Tumoral non‐amyloidotic monoclonal immunoglobulin light chain deposits (‘aggregoma’): presenting feature of B‐cell dyscrasia in three cases with immunohistochemical and biochemical analyses

Abstract

Tumoral monoclonal immunoglobulin (Ig) light chain non-fibrillar deposits ('aggregomas'), which can be considered analogous to solitary light chain amyloidomas, are a rare presenting feature of B-cell dyscrasias. It is not certain if they are truly localized or if in reality they represent an initial expression of a silent systemic non-amyloid light chain deposition disease (LCDD). This report describes three patients, two of whom presented with cervical masses and the third with a solitary lung nodule, each comprising granular aggregates of monoclonal kappa light chain. Extracted deposits from the lymph node of one patient were shown by N-terminal amino acid sequence analysis to belong to the variable-region kappa I (Vkappa I) light chain subgroup, the first reported kappa-LCDD protein encoded by the L9 gene and the first report of an expressed protein related to this gene. Extracted deposits from the lung nodule of the second patient belonged to the Vkappa IV light chain subgroup encoded by the B3 germ line gene. The N-terminal amino acid sequences of the light chains from the aggregomas were compared with the related germ line sequences and to the N-terminal amino acid sequences of the nine other known kappa-LCDD light chains reported thus far from patients with systemic LCDD.